Diamond bit

ABSTRACT

A diamond bit, the diamonds in the sidewall thereof being set in a blunt position in a direction radial to the central axis of the bit as well as in a cutting position in a direction tangential to a helical line passing through the cutting tip of the diamond and having a central axis coinciding with the central axis of the bit.

llmted States Patent 1151 3,699,956 Feenstra Feb. 8, W72

[54] DIAMOND BIT [56] References Cited v [72] Inventor: Robiin Feenstra, Rijswijk, Netherlands UNITED STATES PATENTS Sh ll 0 Com an Ne York, 2,708,105 5/1955 Williams ..l75/330 X [73] Ass'gnee e p w 3,027,952 4/1962 Brooks...; ..175/329 [22] Filed: Dec. 12, 1969 3,318,399 5/1967 Garner 1 75/329 [21 1 884396 Primary Examiner-Emest R. Purser Attorney-T. E. Bieber and J. H. McCarthy 30 F re A lication Prim-i Data 1 o i B ty 22 061/69 [57] ABS CT Apr 3 ma n n A diamond bit, the dlamonds in the sldewall thereof being set 7 3 9,1 5 39 a blunt Position in a direction radial the central axis of l 5/ 1 5 1 the bit as well as in a cutting position in a direction tangential [58] Field 'f E a r l 125/39 to a helical line passing through the cutting tip of the diamond and having a central axis coinciding with the central axis of the bit.

10 Claims, 7 Drawing Figures PATENTED FEB 8872 INVENTORZ ROBIJN FEENSTRA BY I MZM/

HIS ATTORNEY DIAMOND BIT BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to diamond bits, and more particularly to diamond bits such as can be used in well drilling.

2. Summary of the Invention Diamond bits are used in particular for drilling holes through rock material of poor drillability, which is often required when drilling subsurface formations for the purpose of prospecting for and/or recovering oil or other valuable products.

These bits are of the rotary type and the diamonds thereof exert a scraping action on the rock through which a hole is being drilled, the bit being loaded in an axial direction and being rotated around its central axis.

Bits of this type are especially useful for drilling through deep, abrasive, hard formations, since under these operating conditions they have a longer life than any other type of rotary rock bit, such as a roller bit. Consequently, a diamond bit has to be replaced less frequently than a bit of another type. The higher material and manufacturing costs of a diamond bit as compared with other types of bits are easily compensated by the advantages obtained as a result of the reduction in time required to replace the worn bits during drilling operations.

The object of the invention is to provide a diamond bit which is less liable to be damaged by lateral vibrations during drilling than known diamond bits.

A further object is to provide a diamond that which is less liable to wobbling than known diamond bits.

Still a further object of the invention is to provide a diamond bit in which the diamonds are less liable to be crushed or burned than in known diamond bits.

These objects are achieved by designing the bit in such a manner that no oversize-hole cutting will occur when the bit is operated in the formation. Oversize-hole cutting causes the diamonds on the bottom part of the bit or the face of the bit (that is the part of the bit cutting the bottom of the hole) to cut zigzag tracks and to cross each others tracks, thus giving rise to shock loads on the diamonds. Another consequence of oversize-hole cutting is that the bit on being rotated in the hole is subject to wobbling, whereby the diamonds arranged in the face of the bit become overloaded. Still a further consequence of oversize-hole cutting is that the flow of drilling fluid over the surface of the bit and along the diamonds is no longer exclusively controlled by the waterways arranged in the outer wall of the bit body, so that diamonds which are insufficiently cooled owing to the disturbance of the required drilling fluid distribution over the surface of the diamond bit will be burned out.

Design of a diamond bit such that oversize-hole cutting is obviated will prevent lateral vibration, as well as wobbling of the diamond bit during operation, and will further ensure the required distribution of cooling and washing fluid along the cutting tips of the diamonds. It will be appreciated that the lifetime of such a bit is appreciably longer than that of bits which cut an oversize-hole when used in a subsurface formatron.

The diamond bit according to the invention comprises a bit body and means for connecting the body to a tubular string, the body carrying diamonds for cutting a hole in a formation in which the bit is operated by rotation around the central axis thereof. The bit further comprises diamonds arranged in the sidewall of the bit body for cutting the sidewall of the hole, each of these diamonds being set in a blunt position in a direction radial to the central axis of the diamond bit, as well as being set in a cutting position in a direction tangential to a helical line passing through the cutting tip of the diamond and having a central axis coinciding with the central axis of the diamond bit, this tangential direction being taken at the cutting tip of the relevant diamond.

The diamonds arranged in the sidewall of the bit body may touch a conical plane having the central axis thereof coinciding with the central axis of the diamond bit, the conical plane being arranged with the apex thereof in the direction is which the bit is axially loaded duringoperation. The apex angle of this conical plane may be between 010 and 20.

In another embodiment, the diamonds arranged in the sidewall of the bit body may touch a rotational symmetrical plane which is concave with respect to the central axis of the diamond bit and has a central axis coinciding with the central axis of the diamond bit, which plane has tangential cones which are arranged with the apices thereof in the direction in which the bit is axially loaded during operation and have apex angles with a value between 010 and 20.

Some of the diamonds arranged in the sidewall of the bit body may touch a cylindrical plane having a central axis coinciding with the central axis of the diamond bit. These latter diamonds have a cutting diameter which is equal to the largest cutting diameter of the other diamonds arranged in the sidewall, and lie-in the operative position of the bit wherein the central axis thereof is vertically arrangedabove the other diamonds arranged in the sidewall.

The sidewall of the bit body may comprise further diamonds, which touch a conical plane having a central axis coinciding with the central axis of the diamond bit and being arranged with the apex thereof in a direction opposite to the direction in which the bit is axially loaded during operation, these diamonds being arranged in a position lyingin the operative position of the bit wherein the central axis is vertically arrangedabove the plane passing through the upper diamonds which are arranged in the sidewall of the body to cut the sidewall of the hole.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a side view of a diamond bit according to the invention;

FIG. 2 is a longitudinal cross section of the bit shown in FIG. 1 taken in the direction of the arrows 22;

FIG. 3 is a horizontal section of the bit shown in FIG. 1 taken in the direction of the arrows 33;

FIG. 4 shows an enlargement of the diamond which is located at the intersection of section 22 and section 33 in FIG. 1;

FIG. 5 shows a longitudinal cross section through the diamond shown in FIG. 4 in the direction of the arrows 55;

FIG. 6 shows a horizontal cross section through the diamond shown in FIG. 4 in the direction of the arrows 66; and

FIG. 7 represents an alternative of detail A in FIG. 2 on a larger scale than FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the invention shown by way of example in FIGS. 1-3 of the drawing comprises a bit body ll formed by a wear-resistant material, in which body diamonds 2 are set. These diamonds are grouped alongside waterways 3 via which drilling liquid is passed to cool the diamonds 2 and keep them clean from drilling flour and cuttings. The liquid further cools the bit body II and carries away the rock cut by the diamonds 2. The bit body 1 may consist of tungsten carbide grains which are sintered together and to the steel shank 4 in a known manner such as that of Feenstra, US. Pat. No. 3,453,719. The diamonds 2 are set in the bit body I and the waterways 3 are formed in the mass of tungsten carbide particles before the sintering process is carried out. Since these techniques are known, they are not described here in detail.

The steel shank 4 comprises a coupling 5 provided with connecting means such as screw thread 6 suitable for connecting the diamond bit to a drill collar string (not shown) or other tubular string. If desired, the steel shank 4 may be connected directly to the shaft of a hydraulic turbine or an electric motor suitable for being operated in a borehole. The shank 4 is further provided with a central channel 7 for passing drilling liquid from the interior of the tubular string connected to the screw thread 6 of the coupling 5, to the waterways 3 arranged in the surface of the bit body I.

The center part of the bit body 1 has a conically shaped introversion 8 (FIG. 2) and a channel 9 is provided connecting the channel 7 in the shank 4 with the apex of the conically shaped introversion 8. Since the channel 9 is not concentrically arranged with respect to the central axis of the bit body I, no core will be formed from the formation when the bit according to the invention is being operated in a subsurface formation.

The waterways 3 run from the channel 9 over the curved face of the bit body I and over the sidewall 11 (also indicated by gauge" side).

The exact position of the diamonds in the sidewall 11 will now be described with reference to the FIGS. 4, 5 and 6, which show a diamond corresponding to that in FIG. 1, which is located at the intersection of the sectional planes 2-2 and 3-3.

FIG. 4 is an enlargement of this diamond in the position shown in FIG. 1, and FIGS. 5 and 6 are cross sections thereof, respectively, along sectional planes 55 and 6-6 in FIG. 4.

The diamond 12 shown in FIG. 4 is approximately cubeshaped and located with a fiat plane thereof in the surface of the sidewall 11 (FIGS. 5 and 6). This means that the diamond is set in a blunt position in a direction radial to the central axis (not shown) of the diamond bit. Thus, the diamond cannot exert any cutting action as a result of load being exerted on the diamond 12 in a direction not coinciding with this central axis.

It can further be seen that in the position shown in FIG. 4, the lower plane of the diamond 12 makes an angle B with the horizontal line 13. This angle B may be in the order of 0 to 30, and if desired even be negative. Consequently, on movement of the diamond 12 in the direction of arrow 14 (being the movement of rotation of the diamond bit) the tip 15 of the diamond 12 is in a cutting position when load is exerted thereon in a direction axial to the central axis of the bit. It will be appreciated that the diamond 12 set in the sidewall 11 of the bit body 1 is thus in a cutting position in a direction tangential to a helical line passing through the cutting tip 15 of the diamond 11 and having an axis coinciding with the central axis of the diamond bit, this tangential direction being taken at the cutting tip 15 of the diamond 12. It will be appreciated that if the angle B is negative, the comer 15A of the diamond 12 will act as a cutting tip. It will further be appreciated that what has been described with reference to the diamond 12 shown in FIGS. 4-6, also applies to all the other diamonds 2 set in the sidewall 11 of the bit body 1, which diamonds willwhen the diamond bit is operated in a subsurface formation cut the wall ofthe hole which is then being drilled by the bit.

The angle between the surface of the sidewall 11 and the central axis of the diamond bit is indicated by C in FIG. 5. Since in the embodiment shown in FIGS. 1-6 of the drawing, the sidewall I I of the diamond bit is conical, the apex angle of the cone on which the sidewall 11 is located is twice the value of the angle C. This value preferably may be between 05' and 10. It will be appreciated that the value of angle B increases with increasing values of the angle C.

The relationship between the cutting diameters of the diamonds of the diamond bit will now be described.

The expression cutting diameter of a diamond is understood to mean the diameter of a circle in a plane perpendicular to the central axis of the diamond bit in which the relevant diamond is located and along which circle the cutting tip of the diamond travels during rotation of the bit around its central axis.

When the bit shown in FIGS. 1-3 is operated in a subsurface fonnation, the diamonds set in the bottom portion 10 of the bit body 1 will cut the bottom of a hole, whereas the diamonds set in the sidewall 11 will cut the sidewall of this hole. It will be clear that the hole which is being drilled by the diamonds set in the bottom part 10 of the diamond bit will be enlarged in diameter by the action of the diamonds set in the sidewall 11. The sidewall 11 being of conical shape, this enlargement takes place gradually since the diamonds placed at higher levels of the sidewall show an increase in the cutting diameter thereof.

Since the diamonds set in the sidewall 11 of the bit are set in a blunt position in a direction radial to the central axis of the diamond bit a hole results from the operation of the bit in a subsurface fonnation, wherein all the diamonds arranged in the sidewall 11 are in contact with the wall of the hole. The horizontal components of loads exerted by the drill string and the drill collar string on the bit in directions other than the central axis of the bit will be taken up in the contact plane between the sidewall 11 and the wall of the hole without any cutting action occurring in direction radial with respect to the central axis of the diamond bit. Thus, the contact between the diamonds in the sidewall 11 and the wall of the hole will be maintained in all circumstances without oversize-hole cutting being caused thereby.

The advantages are threefold. In the first place, the diamonds of the bottom part 10 of the bit remain in their own track and cannot cut zigzag tracks and cross each others tracks, which would occur if the hole was oversize and would result in shock loads being exerted on the diamonds. Secondly, the fluid flow across the surface of the bit remains controlled exclusively by the waterways 3, because the bit profile fits the hole profile in the absence of oversize cutting. Consequently, each diamond will be adequately cooled and there will be no burning of the diamonds such as often occurs when an oversize hole is being drilled. Thirdly, the stabilization of the string is better than in an oversized hole, as a result of which wobbling of the bit is reduced and the life of the diamonds is prolonged.

It will further be appreciated that the form of the sidewall 11 of the drill bit is not restricted to a conical plane as described with reference to FIGS. 1-6. With equally favorable results, this sidewall may be formed by a rotational symmetrical plane obtained by rotating a slightly curved line around the central axis of the bit. This sidewall must have a positive curvature, and the diameter of the bit body in cross sections perpendicular to the central axis of the bit has to increase in an upward direction. To prevent heavy axial loads on the diamonds in the sidewall, the projection of this sidewall on the bottom of the hole should be relatively small. This means that the apex angles of the cones which can be arranged tangentially to this sidewall should be small, preferably in the order of 0 IO'-20. These cones are arranged with the apices thereof in the direction wherein the bit is axially loaded.

If a hole has been undercut by a previous bit, those diamonds of a new bit which have the largest cutting diameter will be excessively loaded when this new bit is run into the hole. Some of these diamonds may be crushed or broken out and to prevent undercutting of the hole by this new bit it is advisable to have some more diamonds with a cutting diameter equal to this largest cutting diameter located above the diamonds in the sidewall of the bit. Although a single diamond above each row of diamonds arranged along a waterway may be sufiicient for the purpose, more than one diamond, for example, four or five, may be applied. These diamonds are arranged in the sidewall of the bit and touch a cylindrical plane having a central axis coinciding with the central axis of the bit. Like the diamonds ananged in the sidewall of the bit for cutting the wall of the hole when the bit is being operated, each diamond arranged in the cylindrical part of the sidewall and having a cutting diameter which is equal to the largest cutting diameter of the other diamonds arranged in this sidewall is set in a blunt position in a direction radial to the central axis of the diamond bit, and is set in a cutting position in a direction tangential to a helical line passing through the cutting tip of the diamond and having an axis coinciding with the central axis of the diamond bit, this tangential direction being taken at the cutting tip of the relevant diamond.

Retrieval of the bit from the hole may be made easier by providing the upper part of the bit body with a conically shaped part, which part may be provided with diamonds touching the conical surface. These diamonds may be set sharp and/or blunt.

The three above-mentioned features will now be described with reference to an embodiment which shows all these features. It will, however, be clear that these three features need not be applied together. FIG. 7 of the drawing shows part of a sidewall of a bit, which part can be considered as an altemative of detail A of the cross section of the bit shown in FIG. 2, but on a larger scale. The cross section shown in FIG. 7 is taken over a row of diamonds instead of over a waterway as is the casein FIG. 2.

The shank 20 shown in FIG. 7 carries a bit body 21 made of wear-resistant material and carrying diamonds touching the outer surface thereof. This surface is divided into four zones 22, 23, 24 and 25.

Zone 22 is the lower or bottom part of the bit body carrying diamonds 26 which are set so as to cut the bottom of the hole when the bit is operated in a subsurface formation.

Zone 23 is that part of the sidewall which carries diamonds 27 each of which is set blunt in a radial direction, and sharp in a direction tangential to a helical line passing through the cutting tip of the diamond and having an axis coinciding with the central axis of the bit. All the details given with reference to the diamond 12 in FIGS. M also apply to these diamonds, except, however, that the diamonds 27 do not touch a conical plane, but a rotational symmetrical plane 28, which is concave with respect to the central axis of the diamond bit and has a central axis coinciding with the central axis of the diamond bit. This plane 28 further has cones (not shown) touching the plane, which cones are arranged with the apices thereof in the direction in which the bit is axially loaded during operation, and which cones preferably have apex angles with a value between 010 and 20.

Zone 24 is that part of the sidewall which carries diamonds 29, each of which is equal to the uppermost diamond 27 in cutting diameter as well as in setting. Diamond 27' is the uppermost diamond of a row of diamonds 27 located in zone 23 and touching the rotational symmetrical plane 28. The diamonds 29 touch a cylindrical part of the sidewall and are arranged to take over the function of the diamond 27' should this diamond fail. This prevents the hole from being undercut if the diamond 27 and the corresponding diamonds in other rows are burnt or broken out.

Zone 25 is the upper part of the sidewall, which part carries diamonds 31 It will be clear that this part of the sidewall does not cut the wall of the hole when the drilling bit is in operation, but will guide the bit when the latter is being lifted from the hole. The diamonds 30 are set sharp and prevent wearing out of the zone 25 during retrieval of the bit from the hole. Moreover, the bit can be cut free in an upward direction by rotation during retrieval of the bit from the hole.

It will be appreciated that the invention is not limited to the examples described above with reference to the drawing, but that various modifications may be introduced in these examples.

Some of these modifications are mentioned below.

The invention is not limited to bits having a bottom part or lower part and a conical introversion 8 shaped as shown in FIG. 2. Any other form of bottom part or introversion thereof may be applied which is suitable for the purpose.

Furthermore, the invention is neither limited to the number and distribution of the diamonds over the surface of the bits as shown in FIGS. 1-3 and 7, nor to the number and shape of the waterways 3, nor the distribution of these waterways over the surface of the bits as shown in FIGS. 13 and 7.

The apex angle of the conical surface which is touched by the diamonds arranged in the sidewall ll of the bit shown in FIGS. 1-3 preferably may be between 010 and 20. This sidewall 11 may further be extended in an upward direction by a zone 24 as shown in FIG. 7 and/or a zone 25 as is also shown in FIG. 7.

The application of the inventive diamond-studded sidewall which prevents oversize cutting of a borehole is further not restricted to diamond bits having a drilling liquid supply 9 as shown in FIG. 2. If desired, any other suitable supply of drilling liquid may be used. Furthermore, the invention is not restricted to bits which do not leave a core in the center of the hole, but may also be used with core bits, or bits leaving a core of small diameter which is subsequently broken by the action of the bit and the fragments of which are removed via a side opening in the bit.

As shown in FIGS. 4, 5 and 6, the blunt position of a diamond with respect to loads exerted in a direction radial and perpendicular to the central axis of the diamond bit is obtained by placing a substantially flat plane of the diamond in the plane of the sidewall. However, this blunt position may also be obtained by placing the diamond in a dragging position which means that the point of contact between the diamond and the conical plane is the trailing part of the diamond when viewed in the direction of movement of the diamond along the wall of the borehole. This means that the direction of rotation of the diamond bit unit has to be taken into account when placing the diamonds. This direction can be derived from the type of screw thread used. Normally, the bit, the drill collars and the drill pipes are right-hand threaded, which means that the diamond bit unit is rotated clockwise when looking into the hole (arrow 114 in FIG. 4i). The angle R in FIG. 6 indicates the angle between the diamond plane and the conical plane, through which the diamond can be dragged along the wall of the borehole without cutting in a radial direction. The comer 15A of the diamond 12 then acts as cutting tip in a direction tangential to a helical line having a central axis coinciding with the central axis of the bit. This line passes through the tip 15A and the tangential direction is taken at the tip 115A.

Although the diamonds shown in the drawing to which the above examples refer are all approximately cube-shaped, it will be appreciated that differently shaped diamonds may also be used, provided that they are set in such a position that they cut in a direction tangential to a helical line passing through the cutting tip of the diamond and having an axis coinciding with the central axis of the diamond bit unit, this tangential direction being taken at the cutting tip of the relevant diamond, and that they are blunt in a direction radial to the central axis of the diamond bit.

A diamond bit having the diamonds in the sidewall thereof set in accordance with the present invention may be used with advantage in the diamond bit unit described and claimed in copending application No. 839,541, filed July 7, i969 and now US. Pat. No. 3,534,294.

If desired, the diamond bit according to the invention may be used in combination with stabilizers and/or reamers of known design. These known stabilizers may for example be of rubber or hard-faced steel and are carried by the drill string at some distance above the diamond bit according to the invention. They will dampen the oscillating movements of the drill string. The known reamers, if applied, are also located above the diamond bit according to the invention. Since these known reamers have the characteristic feature of being able to cut in directions radial to the central axis of the reamer, the hole is cut to a diameter greater that the outer diameter of the reamer, which has the advantage that thediamond bit (and the rearner) can be lifted very easily from the hole, or run in.

I claim:

I. A diamond bit for drilling a hole in a subsurface formation, said diamond bit having a central axis and comprising:

a bit body;

means carried by the bit body for connecting the bit body to a tubular drill string;

diamonds set in the bottom part of the bit body to cut the bottom of the hole when used therein;

sidewall diamonds set in the sidewall of the bit body to cut the sidewall of the hole, each of said sidewall diamonds being positioned at a cutting diameter on the bit body and being set in a blunt position in a direction radial to the central axis of the diamond bit as well as in a cutting position in a direction tangential to a helical line passing through the cutting tip of that sidewall diamond and having a central axis coinciding with the central axis of the diamond bit, this tangential direction being taken at the cutting tip of the sidewall diamond.

2. The diamond bit of claim 1 wherein the diamond bit comprises additional diamonds set in the upper part of the sidewall of the bit body which additional diamonds touch a conical plane having a central axis coinciding with the central axis of the diamond bit, this conical plane being arranged with the apex thereof in a direction opposite to the direction in which the bit is axially loaded during operation, said additional diamonds being positioned at cutting diameters no greater than the largest cutting diameter of said first-mentioned sidewall diamonds set in the sidewall of the bit body.

3. The diamond bit of claim 1, wherein at least some of the sidewall diamonds set in the sidewall of the bit body touch a conical plane having the central axis thereof coinciding with the central axis of the diamond bit, this conical plane being ar ranged with the apex thereof in the direction in which the bit is axially loaded during operation.

4. The diamond bit of claim 3, wherein the apex angle of the conical plane is between 10 and 20.

5. The diamond bit of claim 1, wherein at least some of the sidewall diamonds set in the sidewall of the bit body touch a rotational symmetrical plane which is concave with respect to the central axis of the diamond bit, which has a central axis coinciding with the central axis of the diamond bit, and which can be arranged tangentially to a group of conical surfaces having the central axis thereof coinciding with the central axis of the diamond bit and the apices thereof in the direction in which the bit is axially loaded during operation.

6. The diamond bit of claim 5, wherein the group of conical surfaces to which the rotational symmetrical plane can be tangentially arranged consists of cones which have apex angles between 010 and 20.

7. The diamond bit of claim 3 wherein at least some additional sidewall diamonds set in the sidewall of the bit body touch a cylindrical plane intersecting the conical plane and having a central axis coinciding with the central axis of the diamond bit, said additional diamonds being positioned at cutting diameters equal to the largest cutting diameter of all other diamonds arranged in the sidewall of the bit body.

8. The diamond bit of claim 5 wherein at least some additional sidewall diamonds arranged in the sidewall of the bit body touch a cylindrical plane intersecting the rotational symmetrical plane and having a central axis coinciding with the central axis of the diamond bit, said additional diamonds being positioned at cutting diameters equal to the largest cutting diameter of all other diamonds arranged in the sidewall of the bit body.

9. The diamond bit of claim 1 wherein said sidewall diamonds set in a blunt position in a direction radial to the central axis of the diamond bit have at least one substantially flat plane and wherein said sidewall diamonds are set in said bit body with a substantially flat plane of the sidewall diamond in the plane of the sidewall of the bit body.

10. The diamond bit of claim 1 wherein said sidewall diamonds set in a blunt position in a direction radial to the central axis of the diamond bit have at least one substantially flat plane and wherein said sidewall diamonds are set such that there is a line of contact between the sidewall diamond and the plane of the sidewall at the trailing part of a flat plane of the sidewall diamond with respect to the direction of motion of the sidewall diamond in operation of the diamond bit and such that the leading part of said flat plane of the sidewall diamond is within the bit body. 

1. A diamond bit for drilling a hole in a subsurface formation, said diamond bit having a central axis and comprising: a bit body; means carried by the bit body for connecting the bit body to a tubular drill string; diamonds set in the bottom part of the bit body to cut the bottom of the hole when used therein; sidewall diamonds set in the sidewall of the bit body to cut the sidewall of the hole, each of said sidewall diamonds being positioned at a cutting diameter on the bit body and being set in a blunt position in a direction radial to the central axis of the diamond bit as well as in a cutting position in a direction tangential to a helical line passing through the cutting tip of that sidewall diamond and having a central axis coinciding with the central axis of the diamond bit, this tangential direction being taken at the cutting tip of the sidewall diamond.
 2. The diamond bit of claim 1 wherein the diamond bit comprises additional diamonds set in the upper part of the sidewall of the bit body which additional diamonds touch a conical plane having a central axis coinciding with the central axis of the diamond bit, this conical plane being arranged with the apex thereof in a direction opposite to the direction in which the bit is axially loaded during operation, said additional diamonds being positioned at cutting diameters no greater than the largest cutting diameter of said first-mentioned sidewall diamonds set in the sidewall of the bit body.
 3. The diamond bit of claim 1, wherein at least some of the sidewall diamonds set in the sidewall of the bit body touch a conical plane having the central axis thereof coinciding with the central axis of the diamond bit, this conical plane being arranged with the apex thereof in the direction in which the bit is axially loaded during operation.
 4. The diamond bit of claim 3, wherein the apex angle of the conical plane is between 0* 10'' and 20*.
 5. The diamond bit of claim 1, wherein at least some of the sidewall diamonds set in the sidewall of the bit body touch a rotational symmetrical plane which is concave with respect to the central axis of the diamond bit, which has a central axis coinciding with the central axis of the diamond bit, and which can be arranged tangentially to a group of conical surfaces having the central axis thereof coinciding with the central axis of the diamond bit and the apices thereof in the direction in which the bit is axially loaded during operation.
 6. The diamond bit of claim 5, wherein the group of conical surfaces to which the rotatIonal symmetrical plane can be tangentially arranged consists of cones which have apex angles between 0* 10'' and 20*.
 7. The diamond bit of claim 3 wherein at least some additional sidewall diamonds set in the sidewall of the bit body touch a cylindrical plane intersecting the conical plane and having a central axis coinciding with the central axis of the diamond bit, said additional diamonds being positioned at cutting diameters equal to the largest cutting diameter of all other diamonds arranged in the sidewall of the bit body.
 8. The diamond bit of claim 5 wherein at least some additional sidewall diamonds arranged in the sidewall of the bit body touch a cylindrical plane intersecting the rotational symmetrical plane and having a central axis coinciding with the central axis of the diamond bit, said additional diamonds being positioned at cutting diameters equal to the largest cutting diameter of all other diamonds arranged in the sidewall of the bit body.
 9. The diamond bit of claim 1 wherein said sidewall diamonds set in a blunt position in a direction radial to the central axis of the diamond bit have at least one substantially flat plane and wherein said sidewall diamonds are set in said bit body with a substantially flat plane of the sidewall diamond in the plane of the sidewall of the bit body.
 10. The diamond bit of claim 1 wherein said sidewall diamonds set in a blunt position in a direction radial to the central axis of the diamond bit have at least one substantially flat plane and wherein said sidewall diamonds are set such that there is a line of contact between the sidewall diamond and the plane of the sidewall at the trailing part of a flat plane of the sidewall diamond with respect to the direction of motion of the sidewall diamond in operation of the diamond bit and such that the leading part of said flat plane of the sidewall diamond is within the bit body. 